Throughout this specification, when discussing the application of this invention to the aorta or other blood vessels, the term “distal” with respect to a prosthesis is intended to refer to a location that is, or a portion of the prosthesis that when implanted is, further downstream with respect to blood flow; the term “distally” means in the direction of blood flow or further downstream. The term “proximal” is intended to refer to a location that is, or a portion of the prosthesis that when implanted is, further upstream with respect to blood flow; the term “proximally” means in the direction opposite to the direction of blood flow or further upstream.
The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, the aortic wall can weaken, resulting in an aneurysm. Upon further exposure to hemodynamic forces, such an aneurysm can rupture. One study found that in Western European and Australian men who are between 60 and 75 years of age, aortic aneurysms greater than 29 mm in diameter are found in 6.9% of the population, and those greater than 40 mm are present in 1.8% of the population.
One surgical intervention for weakened, aneurysmal or ruptured vessels involves the use of an endoluminal prosthesis to provide some or all of the functionality of the original, healthy vessel and/or preserve any remaining vascular integrity by replacing a length of the existing vessel wall that spans the site of vessel failure.
It is preferable that these prostheses seal off the failed portion of the vessel. For weakened or aneurysmal vessels, even a small leak in the prosthesis may lead to the pressurization of or flow in the treated vessel, which aggravates the condition the prosthesis was intended to treat. A prosthesis of this type can, for example, treat aneurysms of the abdominal aortic, iliac, or branch vessels such as the renal arteries.
An endoluminal prosthesis can be of a unitary construction, or be comprised of multiple prosthetic modules. A modular prosthesis allows a surgeon to accommodate a wide variation in vessel morphology while reducing the necessary inventory of differently sized prostheses. For example, aortas vary in length, diameter and angulation between the renal artery region and the region of the aortic bifurcation. Prosthetic modules that fit each of these variables can be assembled to form a prosthesis, obviating the need for a custom prosthesis or large inventories of prostheses that accommodate all possible combinations of these variables. A modular system may also accommodate deployment by allowing the proper placement of one module before the deployment of an adjoining module.
Modular systems are typically assembled in situ by overlapping the tubular ends of the prosthetic modules so that the end of one module sits partially inside the other module, preferably forming circumferential apposition through the overlap region. This attachment process is called “tromboning.” The connections between prosthetic modules are typically maintained by the friction forces at the overlap region and enhanced by the radial force exerted by the internal prosthetic module on the external prosthetic modules where the two overlap. The fit may be further enhanced by stents fixed to the modules at the overlap region.
A length of a vessel which may be treated by these prostheses may have one or more branch vessels, i.e. vessels anastomosed to the main vessel. The celiac, superior mesenteric, left common carotid and renal arteries, for example, are branch vessels of the aorta; the hypogastric artery is a branch vessel of the common iliac artery. If these branch vessels are blocked by the prosthesis, the original blood circulation is impeded, and the patient can suffer. If, for example, the celiac artery is blocked by the prosthesis, the patient can experience abdominal pain, weight loss, nausea, bloating and loose stools associated with mesenteric ischemia. The blockage of any branch vessel is usually associated with unpleasant or even life-threatening symptoms.
When treating a vessel with an endoluminal prosthesis, it is therefore preferable to preserve the original circulation by providing a prosthetic branch that extends from the main prosthetic module to a branch vessel so that the blood flow into the branch vessel is not impeded. For example, the aortic section of the Zenith® abdominal aortic prosthesis (Cook Incorporated, Bloomington, Ind.), described below, can be designed to extend above the renal arteries and to have prosthetic branches that extend into and provide flow to the renal arteries. Alternatively, the iliac branches of a bifurcated aortic prosthesis can be designed to extend into and provide flow to the corresponding hypogastric arteries. Branch extension prosthetic modules (“branch extensions”) can form a tromboning connection to the prosthetic branch to extend further into the branch artery. Furthermore, some aneurysms extend into the branch vessels. Deploying prosthetic branches and branch extensions into these vessels may help prevent expansion and/or rupture of these aneurysms. High morbidity and mortality rates are associated with these aneurysms.
Typically, existing prosthetic branches have a straight y- or t-shaped connection to the main endoluminal graft. Examples of such prosthetic branches and their associated branch extensions are shown in U.S. Pat. Nos. 6,520,988 and 6,579,309. Some of these branch extensions and their associated prosthetic branches may dislocate, kink and/or cause poor hemodynamics. These problems may lead to thrombogenesis and endoleaks at the interconnection of the prosthetic branch and branch extension.